Method of making an intraluminal stent graft

ABSTRACT

A method of making an tubular intraluminal graft in the form of a tubular diametrically adjustable stent having a tubular covering of porous expanded polytetrafluoroethylene which is less than 0.10 mm thick. The covering may be on the exterior surface of the stent, or on the interior surface of the stent, or both. The covering may be affixed to the stent by an adhesive which is preferably fluorinated ethylene propylene.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.10/083,461 (U.S. Pat. No. 6,547,815) which is a continuation of U.S.application Ser. No. 09/306,522 (U.S. Pat. No. 6,357,104) which is adivision of U.S. application Ser. No. 08/872,837 (U.S. Pat. No.5,925,075), which is a continuation of U.S. application Ser. No.08/109,214 (U.S. Pat. No. 5,735,892).

FIELD OF THE INVENTION

[0002] This invention relates to the field of intraluminal grafts andparticularly to a method of making thin-wall intraluminal grafts usefulas an inner lining for blood vessels or other body conduits.

BACKGROUND OF THE INVENTION

[0003] Conventional vascular grafts have long been used for vascularrepair in humans and animals. These devices are typically flexible tubesof woven or knitted polyethylene terephthalate or of porouspolytetrafluoroethylene (hereinafter PTFE). Grafts of biological originare also used, these being typically fixed human umbilical or bovinearteries. These conventional vascular grafts usually require invasivesurgical methods that expose at least both ends of the segment of vesselto be repaired. Frequently it is necessary to expose the entire lengthof the vessel segment. These types of repairs consequently cause majortrauma to the patient with corresponding lengthy recovery periods andmay result in occasional mortality.

[0004] Alternative methods have evolved which use intraluminal vasculargrafts in the form of adjustable stent structural supports, tubulargrafts or a combination of both. These devices are preferably remotelyintroduced into a body cavity by the use of a catheter type of deliverysystem. Alternatively they may be directly implanted by invasivesurgery. The intent of these methods is to maintain patency after anoccluded vessel has been re-opened using balloon angioplasty, laserangioplasty, atherectomy, roto-ablation, invasive surgery, or acombination of these treatments.

[0005] Intraluminal vascular grafts can also be used to repairaneurysmal vessels, particularly aortic arteries, by inserting anintraluminal vascular graft within the aneurysmal vessel so that theprosthetic withstands the blood pressure forces responsible for creatingthe aneurysm.

[0006] Intraluminal vascular grafts provide a new blood contactingsurface within the lumen of a diseased living vessel. Intraluminalgrafts are not, however, limited to blood vessels; other applicationsinclude urinary tracts, biliary ducts, respiratory tracts and the like.

[0007] If the intraluminal graft used is of thin enough wall andadequate flexibility, it may be collapsed and inserted into a bodyconduit at a smaller diameter location remote from the intended repairsite. A catheter type of delivery system is then used to move theintraluminal graft into the repair site and then expand its diameterappropriately to conform to the inner surface of the living vessel.Various attachment methods including the use of adjustable stents may beused to secure the intraluminal graft at the desired location withoutthe necessity of invasive surgery.

[0008] Intraluminal vascular grafts were suggested as early as 1912 inan article by Alexis Carrel (Results of the permanent intubation of thethoracic aorta. Surg., Gyn and Ob. 1912;15:245-248). U.S. Pat. No.3,657,744 to Ersek describes a method of using one or more adjustablestents to secure a flexible fabric vascular graft intraluminally, thegraft and stent having been introduced distally and delivered to thedesired position with a separate delivery system.

[0009] Choudhury, U.S. Pat. No. 4,140,126, describes a similar method ofrepairing aortic aneurysms whereby a polyethylene terephthalate vasculargraft is fitted at its ends with metal anchoring pins and pleatedlongitudinally to collapse the graft to a size small enough to allow fordistal introduction.

[0010] Rhodes, U.S. Pat. No. 5,122,154 and Lee, U.S. Pat. No. 5,123,917,describe endovascular bypass grafts for intraluminal use which comprisea sleeve having at least two diametrically-expandable stents. Rhodesteaches that the sleeve material is to be made of conventional vasculargraft materials such as GORE-TEX® Vascular Graft (W. L. Gore &Associates, Inc., Flagstaff Ariz.) or Impra® Graft (Impra, Inc. TempeAriz.). Both the GORE-TEX Vascular Graft and Impra Graft are extrudedand longitudinally expanded PTFE tubes. Additionally, the GORE-TEXVascular Graft possesses an exterior helical wrapping of porous expandedPTFE film. The difficulty with the use of either the GORE-TEX VascularGraft or the Impra graft as the sleeve component is that the relativelythick, bulky wall of the extruded, longitudinally expanded PTFE tubeslimits the ability of the tube to be contracted into a smallcross-sectional area for insertion into a blood vessel. For example, thewall thickness of a 6 mm inside diameter Thin Walled GORE-TEX VascularGraft is typically 0.4 mm. The thinness of the wall is limited by thedifficulty of manufacturing an extruded, longitudinally expanded tubehaving a thin wall of uniform thickness.

SUMMARY OF THE INVENTION

[0011] The present invention is a method of making a tubularintraluminal graft comprising a tubular, diametrically adjustable stenthaving an exterior surface, a luminal surface and a wall having amultiplicity of openings through the wall, and further having a tubularcovering of porous expanded PTFE film affixed to the stent, saidcovering being less than about 0.10 mm thick.

[0012] Porous expanded PTFE film has a microstructure of nodesinterconnected by fibrils and is made as taught by U.S. Pat. Nos.3,953,566; 4,187,390 and 4,482,516. As will be described further, thefibrils may be uniaxially oriented, that is, oriented in primarily onedirection, or multiaxially oriented, that is, oriented in more than onedirection. The term expanded is used herein to refer to porous expandedPTFE. The terms expand, expanding and expandable are used herein torefer to diametrically adjustable intraluminal stents. Morespecifically, the term balloon-adjustable refers to stents of the Palmaztype as taught by U.S. Pat. No. 4,776,337 which typically require aballoon catheter to increase the diameter of the stent within a bloodvessel. The term self-expanding refers to stents which increase indiameter by various other means. Stents of this type include stents ofbraided wire made as taught by Wallsten, U.S. Pat. No. 4,544,771; andstents of formed wire made as taught by Gianturco, U.S. Pat. No.4,580,568. Stents of this type expand to a larger diameter after beingreleased from a constraining force which restricts them to a smallerdiameter. Self-expanding stents also include stents formed from Nitinolwire made as taught by PCT US 92/03481. These stents expand in diameterwhen exposed to a slight increase in temperature.

[0013] The tubular covering of porous expanded PTFE film may be affixedto either the exterior surface or the luminal surface of the stent.Alternatively, a first tubular covering of porous expanded PTFE film maybe affixed to the exterior surface of the tubular diametricallyadjustable stent and a second tubular covering of porous expanded PTFEfilm may be affixed to the luminal surface of the tubular diametricallyadjustable stent. The first and second tubular coverings of porousexpanded PTFE film may be affixed to each other through the openingsthrough the wall of the stent.

[0014] The porous expanded PTFE film may be affixed to the stent with anadhesive. The adhesive may be a thermoplastic adhesive and morepreferably a thermoplastic fluoropolymer adhesive such as fluorinatedethylene propylene (hereinafter FEP) or perfluoroalkoxy (hereinafterPFA). Where first and second tubular coverings of expanded PTFE film areaffixed to each other through the multiplicity of openings in the stentwall, the two coverings may be affixed by heating them above thecrystalline melt point of the PTFE film adequately to cause them tothermally adhere, or alternatively they may be affixed by an adhesivesuch as FEP.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a side view of a typical diametrically adjustable stent.

[0016]FIG. 2 is an enlarged schematic representation of themicrostructure of porous expanded PTFE film having a microstructure withuniaxially-oriented fibrils as used to construct Examples 1 and 3.

[0017]FIGS. 3A and 3B describe enlarged schematic representations of themicrostructure of porous expanded PTFE film having microstructures ofmultiaxially-oriented fibrils as used to construct Example 2.

[0018]FIG. 4 is a transverse cross section of the stent of Example 1having a luminal layer of porous expanded PTFE film withlongitudinally-oriented fibrils and an exterior layer of porous expandedPTFE film with circumferentially-oriented fibrils.

[0019]FIG. 5 is a transverse cross section of the stent of Example 2having a luminal layer of porous expanded PTFE film withbiaxially-oriented fibrils.

[0020]FIG. 6 is a transverse cross section of the stent of Example 3having an exterior layer of porous expanded PTFE film withcircumferentially-oriented fibrils.

[0021]FIG. 7 describes a method of collapsing a previously outwardlyadjusted balloon-expandable stent.

[0022]FIG. 8 describes the fitting of a single tubular sleeve to boththe exterior and luminal surfaces of a stent.

[0023]FIG. 9 describes the removal a covered, braided wire stent of theself-expanding type from a manufacturing mandrel by everting the braidedwire, thereby placing the covering on the luminal surface of the stent.

DETAILED DESCRIPTION OF THE INVENTION

[0024]FIG. 1 is a side view of a typical diametrically adjustable stent.The stent is shown as it would appear implanted into a body conduit withits diameter adjusted beyond the collapsed pre-implantation diameter.While the stent shown is made from metal wire, a perforated sleevehaving perforations of suitable shape, size and quantity may also beused. Various suitable stents are described by U.S. Pat. No. 4,776,337to Palmaz and PCT US 92/03481 to Hess. These stents may be made fromimplantable metals such as titanium, stainless steel, or Nitinol.

[0025] The stent may be provided with an exterior covering of porousexpanded PTFE film, or a luminal covering of porous expanded PTFE film,or with both exterior and luminal coverings. Uniaxially-oriented filmshaving a microstructure of uniaxially-oriented fibrils whereinsubstantially all of the fibrils are oriented parallel to each other maybe used. Multiaxially-oriented films having a microstructure ofbiaxially or multiaxially-oriented fibrils wherein the fibrils areoriented in at least two directions which are substantiallyperpendicular to each other may also be used.

[0026]FIG. 2 describes an enlarged schematic representation of themicrostructure of nodes 11 connected by fibrils 12 of a film 20 whereinthe uniaxially-oriented fibrils 12 are substantially parallel to eachother. FIGS. 3A and 3B describe enlarged schematic representations ofalternative microstructures of porous expanded PTFE films that may alsobe used for making the present invention. These microstructures havenodes interconnected by fibrils wherein the fibrils are oriented in atleast two directions which are substantially perpendicular to eachother. FIG. 3A describes a microstructure 30 of nodes 11 and fibrils 13and 15 wherein the fibrils 13 and 15 are biaxially-oriented fibrilswhich are oriented in two different directions that are substantiallyperpendicular to each other. Those microstructures may contain somefibrils 17 which are not oriented in the two different directions. FIG.3B describes another alternative microstructure 35 wherein the fibrils21 are multiaxially-oriented fibrils oriented in virtually alldirections within the plane of the sheet material. Either of these filmsmay be made by having been expanded two directions that areperpendicular to each other. The microstructure 30 ofmultiaxially-oriented fibrils 21 may also have been made by beingexpanded in more than two directions as shown by FIG. 3B. Themanufacture of these films is taught by U.S. Pat. Nos. 3,953,566;4,198,390 and 4,482,516.

[0027] The fibril lengths of the porous expanded PTFE films referred toherein were estimated mean values obtained by examining scanningelectron photomicrographs of these films. For multiaxially-orientedfilms, these estimates included consideration of fibrils oriented in alldirections. The mean fibril lengths of the films used to construct theintraluminal grafts of the present invention are preferred to be withinthe range of about 5 to about 120 microns, although fibril lengthsbeyond this range may also be useful.

[0028] Wall thickness measurements of intraluminal graft stent coveringswere determined by cutting away a portion of the covering that coveredan opening through the stent wall. The thickness of the sample portionwas measured by placing the sample portion between the pads of aMitutoyo model no. 804-10 snap gauge having a part no. 7300 frame, andgently easing the pads into contact with the sample portion until thepads were in full contact with the sample portion under the full forceof the spring-driven snap gauge pads. Film density measurements werebased on the bulk volume of a film sample using the snap-gauge thicknessmeasurement.

[0029] The following examples of intraluminal stent grafts are intendedto be illustrative only and are not intended to limit the scope of theinvention to only the constructions described by these examples.

EXAMPLE 1

[0030] A Nitinol wire stent 10 (Nitinol Medical Technologies, Boston,Mass.) of the type described by FIG. 1 was provided with both a luminalcovering and an exterior covering of expanded PTFE film. This 3 cm longstent was formed from 0.25 mm diameter Nitinol wire into a tubular shapeof interlocking hexagons. The luminal and exterior coverings were bothmade from a uniaxially-oriented film having fibrils orientedsubstantially in a single direction wherein the fibrils were allsubstantially parallel to each other. The luminal covering was providedwith the fibrils oriented parallel to the longitudinal axis of thetubular stent; the exterior covering was provided with the fibrilsoriented substantially circumferential to the tubular stent. The filmused for both the luminal and exterior coverings was a porous expandedPTFE film having a discontinuous, porous coating of FEP applied to oneside of the porous expanded PTFE film. Examination of the FEP coatedside of the film by scanning electron microscopy revealed FEP on onlysmall portions of the nodes and fibrils at the surface of the film. Itwas estimated that less than 10% of the available node and fibrilsurface area exposed at the surface of the film was covered by FEP. Thepresence of the FEP adhesive thus had little or no adverse effect on theporosity of the porous PTFE film.

[0031] The FEP-coated porous expanded PTFE film was made by a processwhich comprises the steps of:

[0032] a) contacting a porous PTFE film with another layer which ispreferably a film of FEP or alternatively of another thermoplasticpolymer;

[0033] b) heating the composition obtained in step a) to a temperatureabove the melting point of the thermoplastic polymer;

[0034] c) stretching the heated composition of step b) while maintainingthe temperature above the melting point of the thermoplastic polymer;and

[0035] d) cooling the product of step c).

[0036] In addition to FEP, other thermoplastic polymers includingthermoplastic fluoropolymers may also be used to make this coated film.The adhesive coating on the porous expanded PTFE film may be eithercontinuous (non-porous) or discontinuous (porous) depending primarily onthe amount and rate of stretching, the temperature during stretching,and the thickness of the adhesive prior to stretching.

[0037] The discontinuously FEP-coated porous expanded PTFE film used toconstruct this example was of about 0.01 mm thickness and had a densityof about 0.3 g/cc. The microstructure of the porous expanded PTFEcontained fibrils of about 50 micron mean fibril length.

[0038] A 3.0 cm length of film 20 having uniaxially-oriented fibrils waswrapped as a single layer 41 around a hollow, tubular, 1.5 cm outsidediameter mandrel 43 of non-porous PTFE to form a seam 45 as described bythe cross section of FIG. 4. The seam edges 45 overlapped as shown byabout 3 mm. The fibrils of the film were oriented parallel to thelongitudinal axis of the mandrel; the FEP-coated side of the film facedaway from the surface of the mandrel. The Nitinol stent was carefullyfitted over the film-wrapped portion of the mandrel. The 3 cm length ofthe stent was centered over the 3.0 cm length of film-wrapped mandrel.The stent was then provided with an exterior covering 47 of a 3.0 cmwide tape of the film described above by wrapping the tapecircumferentially around the exterior surface of the mandrel so that theedges of the circumferentially-wrapped tape overlapped by about 3 mm toform seam 49. The circumferentially wrapped covering was oriented sothat the FEP-coated side of the tape faced inward in contact with theexterior surface of the stent and the outward facing FEP-coated surfaceof the luminal layer of film exposed through the openings in the stent.Except for the overlapped seam edges 49, the circumferentially-wrappedcovering was only one film layer thick. The uniaxially-oriented fibrilsof the microstructure of the circumferentially-wrapped tape werecircumferentially-oriented about the exterior stent surface.

[0039] The film-wrapped mandrel assembly was placed into an oven set at360° C. for a period of 4 minutes after which the film-wrapped mandrelwas removed from the oven and allowed to cool. Following cooling toapproximately ambient temperature, the mandrel was removed from thefilm-wrapped stent. The amount of heat applied was adequate to melt theFEP-coating on the porous expanded PTFE film and thereby cause adjacentlayers of film to adhere to each other. Thus the luminal layer of filmwas adhered to the exterior circumferentially wrapped layer through theopenings between the adjacent wires of the stent. The combined thicknessof the luminal and exterior coverings was about 0.025 mm.

[0040] The film-covered stent was then chilled in a bath of ice waterwhile being rolled between human fingers applying compressiondiametrically across the stent. This reduced the outside diameter of thestent to about 0.3 cm. The collapsed stent was then heated by immersionin about 40° C. water, thereby increasing the stent diameter to about1.5 cm. The film covering showed no visible adverse effects from theprocess of shrinking and increasing the stent diameter.

EXAMPLE 2

[0041] A Nitinol wire stent of the same type used for Example 1 wasprovided with a luminal covering of a porous expanded PTFE film having amicrostructure of biaxially-oriented fibrils as shown by FIG. 3A. Thiswas accomplished by wrapping a hollow tubular mandrel of non-porous PTFEwith a layer of porous expanded PTFE film having a continuous(nonporous) coating of FEP with the FEP-coated side of the film facingoutwardly away from the mandrel surface. This film was about 0.02 mmthick; the porous expanded PTFE had a microstructure ofuniaxially-oriented fibrils with the fibrils oriented circumferentiallyabout the exterior surface of the mandrel. The Nitinol stent wascarefully fitted over the film-wrapped portion of the mandrel. Themandrel assembly was then placed into an oven set at 360° C. for fourminutes. After removal from the oven and subsequent cooling, the mandrelwas removed from the stent leaving the wrapped film adhered to theluminal surface of the stent. This film was then peeled from the luminalstent surface, leaving the FEP-coating and some small shreds of residualporous expanded PTFE adhered to the luminal surface of the stent wires.By removing the film and leaving the FEP adhesive on the luminal stentsurface, the film served only as a release substrate for the applicationof the adhesive to the stent surface.

[0042] As shown by FIG. 5, the mandrel 43 was then provided with asingle layer 51 wrapping of a porous expanded PTFE film 35 having amicrostructure of biaxially-oriented fibrils. This film was of about 30micron fibril length, about 0.08 mm thickness, about 0.3 g/cc densityand did not have an FEP coating. The biaxially-oriented fibrils wereoriented to be substantially parallel to the longitudinal axis of themandrel and to the circumference of the mandrel.

[0043] The film was overlapped adequately to form a 2 mm wide,longitudinally oriented seamline 45 parallel to the longitudinal axis ofthe mandrel. A sheet of polyamide film was temporarily placed over thesurface of the seam and then contacted with the surface of a hand-heldiron set at 400° C. to cause the PTFE film seam edges to adhere to eachother. Excess material beyond the 2 mm wide seam was trimmed away anddiscarded. The stent was again carefully fitted over the film-coveredmandrel. The resulting assembly was placed into an oven set at 380° C.for three minutes and then removed and allowed to cool, after which themandrel was removed from the stent. The porous expanded PTFE filmappeared to be well adhered to the luminal surface of the wire stent bythe FEP coating left from the first, previously removed, layer of film.The wall thickness of the PTFE film covering was about 0.08 mm.

[0044] The film-covered stent was then chilled in a bath of ice waterwhile being rolled between human fingers applying compressiondiametrically across the stent. This reduced the outside diameter of thestent to about 0.3 cm. The collapsed stent was then heated by immersionin about 40° C. water, thereby increasing the stent diameter to about1.5 cm. The film covering showed no visible adverse effects from theprocess of shrinking and increasing the stent diameter.

EXAMPLE 3

[0045] A Palmaz stent of the balloon-expandable type (part no. PS30,Johnson & Johnson Interventional Systems, Inc., Warren, N.J.) wasadjusted from its collapsed outside diameter of 3.4 mm to an enlargedoutside diameter of 8.0 mm by inserting a tapered stainless steelmandrel followed by a straight 8.0 mm diameter stainless steel mandrel.This stent was then provided with a single layer exterior wrapping ofthe same discontinuously FEP-coated, porous expanded PTFE coating usedfor the exterior wrapping of the stent of Example 1. This wasaccomplished by wrapping the film about the exterior surface of themandrel with the uniaxially-oriented fibrils of the film microstructureoriented parallel to the longitudinal axis of the stent. This exteriorcovering 61 is described by the transverse cross section of FIG. 6. A 2mm wide seam 45 was formed from the overlapped edges of the porousexpanded PTFE film 20 by temporarily placing a thin sheet of polyamidefilm over these edges and applying heat from a hand-held iron with asurface temperature of about 400° C. The film-wrapped stent 65 was thenplaced into an oven set at 380° C. for 3 minutes, after which it wasremoved and allowed to cool. The film appeared to be well adhered to theexterior surface of the stent. The wall thickness of the film coveringwas about 0.01 mm. The enlarged stent was then collapsed by thefollowing process.

[0046] A series of 20 cm long 6-0 sutures were tied individually to eachof the closed metal stent openings adjacent to one end of a stent. Thefilm-covered stent was provided with a temporary non-adhered additionalwrapping of longitudinally-oriented film without FEP and having amicrostructure of uniaxially-oriented fibrils. This temporary wrappingwas intended as a dry lubricant. As described by FIG. 7 which omits theexterior film covering for clarity, the enlarged stent 71 was thenpulled by these sutures 77 through a tapered die 75 of round crosssection and 2.5 cm length, the die having a tapered orifice with a 9.5mm diameter bore at its entrance 78 and a 4.5 mm diameter bore at itsexit 79. The result was that the stent was collapsed back to an outsidediameter of 4.5 mm. The lubricity of the temporary covering of porousexpanded PTFE film aided in making it possible to pull the stent throughthe die. This temporary covering was removed after completion of thecollapsing process. It is anticipated that the use of a tapered diehaving an appropriately sized, smaller diameter exit bore would resultin collapsing the stent to its original collapsed diameter. Thefilm-covered stent was again enlarged to a diameter of 8 mm using aballoon catheter followed by a tapered stainless steel mandrel. Thecovering of porous expanded PTFE film appeared to be fully intact afterthe collapsing and enlarging of the film-covered stent.

[0047] Stent coverings may be affixed to a stent surface by variationson this method. For example, a tubular sleeve may be made from a film ofporous expanded PTFE and inverted back into itself and fitted over theinner and outer surfaces of a stent as shown by FIG. 8. The inner 83 andouter 85 portions of the tubular sleeve 81 may be thermally adhered toeach other through the openings in the stent wall, or may be adhered tothe stent surfaces by an adhesive such as FEP, or may be affixed to thestent by suturing the open ends 87 of the tube together.

EXAMPLE 4

[0048] A long length of 0.07 mm diameter single strand 304 stainlesssteel wire was provided with a single layer, approximate 1 mm overlapcovering of porous expanded PTFE film by helically wrapping the wirewith a narrow tape cut from a sheet of porous expanded PTFE film. Thetape used was 6 mm wide, 0.01 mm thick, 0.3 g/cc density, and haduniaxially-oriented fibrils of about 50 micron fibril length. Thistape-covered wire was then heated by pulling the wire through the 0.14mm diameter orifice of a 2.5 cm long die heated to 400° C., at a rate of1.5 meters per minute, thereby adhering the overlapped edges of the tapetogether and thereby adhering the tape to the wire. This wire was thencut into shorter lengths and spooled onto 16 bobbins. These bobbins wereused to supply the wire to a model D-5600 Steeger braider.

[0049] A 12 meter length of 1.75 mm diameter non-porous PTFE mandrel wasthen fed into the braider where a braided covering of the above wire wasapplied at a density of about 16 picks/cm. An additional covering oftape cut from a sheet of porous expanded PTFE film was then helicallywrapped over the surface of the wire-braided PTFE mandrel. The tape usedfor this helical wrapping was of 0.01 mm thickness, 0.3 g/cc density,about 50 micron fibril length and 12 mm width. Adjacent edges of thehelical wrapping were overlapped by approximately 1 mm. The wire-braidedTeflon mandrel was then placed into an oven set at 380° C. for fourminutes, after which it was removed and allowed to cool. As shown byFIG. 9, the wire-braided stent 91 with the exterior covering of porousexpanded PTFE tape was then removed from the non-porous PTFE mandrel 93by folding the ends 95 of the braided wires back on themselves andpulling on these everted ends. The exterior covering of porous expandedPTFE film is omitted from FIG. 9 for clarity. By applying tension onthese everted ends in a direction parallel to the longitudinal axis ofthe mandrel and from the everted end back toward the opposite,non-everted end, the entire braided construction was everted andsimultaneously removed from the mandrel. This everting process ofremoving the braided assembly from the mandrel resulted in the helicalwrapping of film being located on the lumen of the stent. Thisconstruction offered good self-expanding characteristics in that whenlongitudinal tension was placed on the stent, the length of the stentincreased and the diameter decreased. Upon release of tension, the stentimmediately recovered its previous shorter length and larger diameter.This film-covered stent is therefore expected to be useful as aself-expanding stent.

I claim:
 1. A method of making a tubular intraluminal graft comprising:a) providing a length of wire; b) providing the length of wire with afirst polymeric covering to create a covered wire; c) braiding thecovered wire to create a tubular form having a wall with a multiplicityof openings therethrough; and d) providing the tubular form with asecond polymeric covering which covers at least some of the openings. 2.A method according to claim 1 wherein said first covering is porouspolytetrafluoroethylene.
 3. A method according to claim 2 wherein saidsecond covering is porous polytetrafluoroethylene.
 4. A method accordingto claim 1 wherein said second covering is porouspolytetrafluoroethylene.